Though we use the term "burn-in" when speaking of cable, it's not technically correct. Nevertheless, we use this term for lack of a more concise, relatable description.
What we are really dealing with is temporary dielectric forming or conditioning if you like.
In a perfect world, the insulators used in our cables would all have a relative permittivity (used to be called "dielectric constant") of 1. Materials with higher relative permittivities (signified by the symbol "
εr
") generally perform worse as insulators. Example
εr
values for common materials: PE = 2.25, rubber = 7, water ~80 (very temperature dependent). Air is very nearly 1.0 and is theoretically considered the best insulator/dielectric for cables; however, it is practically impossible to implement a 100% air insulator in a cable, but
we can get close.
What this all means is that even great insulators in cables such as PE or Teflon have dielectric properties, absorbing energy from adjacent conductors and releasing the energy back into the conductor over time. This has been described as having a "smearing" effect on the signal as the amount of energy varies with frequency, and the time delay of absorption and release varies with frequency. Typically, dielectrics with higher
εr
values will introduce more signal distortion.
As a cable is used
constantly over time, the dielectric insulators are polarized on a molecular level by current passing through the conductors. Eventually, the insulator's molecules become organized so that the so-called "smearing" effects are diminished. The absorption and release of energy by the dielectric is now more uniform. This dielectric conditioning can take days or weeks depending upon many factors such as conductor size/material, dielectric size/material, overall geometry, current, temperature, etc. Here is an excerpt from AQ's
Dielectric Bias System technical paper:
Unlike mechanical burn-in of a car engine or a loudspeaker or NightHawk's drivers, the dielectric in a cable can return back to it's original, unorganized state after a few days or weeks of non-use. This is why "burn-in" or "break-in" does not tell the whole story in regards to cable. We recommend an initial two weeks of constant use to ensure the cable's dielectric insulation is at optimal conditioning. Further, a cable should be kept in frequent (not necessarily constant) use to ensure it remains in its optimal performance condition.
As a cable company, it is AQ's job to literally obsess over these small details. In our world it is the culmination of myriad small details which makes the whole more than the sum of its parts. We find dielectric performance critical to what we do.
That said, the importance of these phenomena are up to the individual listener to decide.